In recent years, the demand for the performance and functions of polymeric materials becomes severe day by day, and especially high balance between contradictory properties is requested. For example, the compatibility between impact resistance and stiffness and the compatibility between weight reduction and strength are required for automobile materials, and the compatibility between impact resistance and heat resistance is required for size reduction of electric and electronic apparatus materials. There is no end to the required compatibility list. Further for promoting the practical use of polymeric materials as commercial products in recent years, active efforts are being made for application as automobile parts, application as sporting goods, application as architectural materials, application as electric and electronic apparatus parts, etc., and among these applications, increasing applications require energy absorbability such as impact absorbability and vibration absorbability.
For example, for application as automobile parts, so-called impact energy absorbing members are proposed in terms of both structures and materials, to be installed between interior parts and car body panels for protecting human bodies from the impacts of collisions. In terms of materials, the impact energy absorbing members are required to have the flexibility of being deformed at low stress without being brittle-fractured even if collisions should occur, and it is necessary to satisfy this property without impairing heat resistance and stiffness. In addition, in recent years, these required properties are more and more sophisticated and diversified, and it is virtually difficult to let one polymer respond to them. Therefore, in recent years, polymer alloy techniques using multiple polymers are main approaches for the development of polymeric materials. Especially at present, active attempts are being made to dramatically improve properties by sophisticated control of morphologies.
For example, disclosed is a method for achieving the compatibility between impact resistance and flexural modulus of elasticity by forming a dispersed phase composed of a rubber component in a continuous phase composed of polypropylene resin and letting a modified polypropylene resin and a compound capable of reacting with the modified polypropylene resin exist in the dispersed phase (JP 08-183887 A). Furthermore, disclosed is a method for improving impact resistance without impairing weather resistance, transparency, scratch resistance and stiffness, by forming a morphology having a micro-phase separated structure compositely containing a portion of a (meth)acrylic polymer component, wherein at least a portion of the (meth)acrylic polymer component and at least a portion of a modified urethane elastomer component are chemically bound to each other (JP 2000-319475 A). Furthermore, disclosed is a method for improving impact resistance, brittle temperature, stiffness, surface hardness and tensile fracture elongation in good balance, by dispersing a hydrogenated block copolymer into a continuous phase composed of a polypropylene-based resin and a dispersed phase composed of a rubbery polymer respectively (JP 2001-106844 A).
Moreover, among polymeric materials, especially engineering plastics are widely used in various industrial fields as structural materials, functional materials, etc., since they are excellent in heat resistance, mechanical properties and impact resistance.
Also with regard to typical engineering plastics such as polyamide resins, since those plastics used respectively alone are limited in practical applications, improvements by alloying with other resins are being made. Especially in recent years, improvements by control of morphologies are actively being made.
As an example of improving properties by controlling the morphology, disclosed is a method for enhancing the impact strength and the surface peel strength of a resin composition consisting of a continuous phase composed of a polyamide resin and a dispersed phase of particles composed of a polyolefin modified by an α,β-unsaturated carboxylic acid, dispersed in the continuous phase, wherein the number average particle size and the particle size distribution of the dispersed phase are controlled (JP 09-31325 A).
Further, disclosed is a method for improving low water absorbability, dimensional stability, stiffness, toughness and moldability in good balance by letting a dispersed phase with a core-shell particle structure consisting of a modified polyolefin and an unmodified polyolefin exist in a continuous phase composed of a polyamide resin (JP 07-166041 A).
Furthermore, disclosed is a resin composition comprising a thermoplastic resin and a reactive functional group-containing resin, excellent in stiffness, impact resistance and appearance after deformation, by forming one of the resins as a continuous phase and the other resin as a dispersed phase or by forming both the resins as continuous phases (co-continuous phase) and letting fine particles of 300 nm or less exist in the continuous phase and the dispersed phase or in the co-continuous phase (JP 2005-187809 A).
Moreover, in recent years, new experimental methods for evaluating and analyzing materials by three-dimensionally and directly observing the real spaces of heterogeneous structures of polymers (three-dimensional imaging or three-dimensional microscopy) attract attention. Methods effective for three-dimensional observation of polymeric materials include confocal laser scan microscopy, X-ray CT, three-dimensional NMR microscopy, transmission electron microscopy tomography (TEMT), etc. Among them, partly because of the recent nanotechnology boom, TEMT with nanometer scale resolution attracts attention. For example, the document of Macromolecules, 36, 6962-6966 (2003) discloses three-dimensional observations and analyses of block copolymers using TEMT.
Further, typical impact absorbing materials include thermoplastic elastomers typified by polyurethane, but they are often limited in the applicable range because of low heat resistance and, in recent years, materials excellent in heat resistance and impact resistance are developed as polymer alloys. Especially U.S. Pat. No. 3,845,163 and JP 51-151797 A disclose thermoplastic compositions excellent in heat resistance and impact resistance, respectively consisting of a polyamide and an ionomer. However, when these materials are subjected to large-load high-speed impacts, they allow a large maximum load to act on the objects protected by them and the materials per se are fractured. So, materials with more excellent impact absorbability are being demanded in this situation.
JP 2005-187809 A discloses a resin composition comprising a thermoplastic resin and a reactive functional group-containing resin excellent in stiffness, impact resistance and appearance after deformation, by forming one of the resins as a continuous phase and the other resin as a dispersed phase or by forming both the resins as continuous phases (co-continuous phase) and letting fine particles of 300 nm or less exist in the continuous phase and the dispersed phase or in the co-continuous phase. Further, JP 2006-89701 A discloses a resin composition and an impact absorbing member that decline in elastic modulus and becomes softer with the increase of stress rate. However, in neither of the resin compositions, no sophisticated structural control is performed in the dispersed phase, and the resin compositions cannot sufficiently absorb large-load high-speed impacts.
However, according to the methods described in JP 08-183887 A and JP 2000-319475 A, a second dispersed phase merely exists in another dispersed phase (first dispersed phase) in a continuous phase, and no sophisticated structural control is performed. So, the effect of improving the mechanical properties is insufficient. Further, according to the method described in JP 2001-106844 A, the second dispersed phase merely (1) exists at the interfaces between the continuous phase and the first dispersed phase and/or (2) deeply penetrates into the first dispersed phase or exists like lakes (like salami), and no sophisticated structural control is performed. So the effect of improving mechanical properties is insufficient. Furthermore, according to the method described in JP 09-31325 A, the basic phase structure is a simple sea-isle structure and, even if impact resistance can be enhanced, there is a problem that other properties decline. Moreover, according to the method described in JP 07-166041 A, the dispersed phase in the continuous phase merely has a core-shell structure, and the balance of mechanical properties is not sufficient. Further, according to the method described in JP 2005-187809 A, fine particles merely exist in the continuous phase/dispersed phase, and the balance of mechanical properties is not sufficient. Furthermore, if the resin compositions described in JP 08-183887 A, JP 2000-319475 A, JP 2001-106844 A, JP 09-31325 A and JP 07-166041 A are pulled at a higher speed in a tensile test, the elastic modulus becomes high, namely, the resin compositions become hard and fragile, showing the behavior as observed with general polymeric materials. On the other hand, if the resin composition described in JP 2005-187809 A is pulled at a higher speed in a tensile test, the elastic modulus declines, namely, the resin composition becomes soft, showing a peculiar viscoelastic behavior. However, since no sophisticated structural control is performed in the dispersed phase, the exhibited peculiar viscoelastic behavior is not sufficiently effective.
Meanwhile, in the conventional use of TEMT, three-dimensional observations and analyses of micro-phase separated structures of block copolymers, etc. have been performed, but in connection with thermoplastic resin compositions, there has been no case where three-dimensionally connective structures containing a continuous phase component formed in the respective dispersed phase particles of a dispersed phase have been confirmed.